In air ventilation systems requiring high efficiency filters such as High-Efficiency Particulate Air (HEPA) filters and other high efficiency filters, it is known to use filter housings with some type mechanical clamping mechanism to secure and effectively clamp and seal the filter within the filter housing. WO2012/134650 discloses a filter frame assembly, which supports the filter and which is movably arranged in the filter housing, with an adjustable mechanical clamping mechanism including a frame having a downstream member coupled to a cross member, the downstream member and the cross member being adapted to fit within the housing. The filter frame assembly comprises at least two clamping mechanisms each coupled to a respective handle which is used to displace a part of the filter frame assembly thereby clamping a filter unit received in a filter receiving aperture defined above the cross-member. When utilizing such mechanical clamping mechanisms to seal high efficiency filters, it is a requisite to ensure that any bypass or leakage around the seal is less than the maximum penetration of the filter.
Filter housings with filter frame assemblies and clamping mechanisms as described above are typically used in critical filtration applications like for instance nuclear, pharmaceutical and risk laboratories. Very high safety standards complying with for instance increasingly stringent requirements from bio-safety authorities are thus applied. Periodic replacement of the filters is required to meet regulatory, and may involve the replacement of a large number of filters on a regular bases. A potential problem with the clamping mechanism of the above type and others is that any mistake made during replacement of the filters in the air ventilation system, e.g. if the filters are not properly positioned, the clamping mechanism are not properly closed etc, could cause leakage of hazardous substances to the surroundings.
Typically, a so called bag-in/bag-out solution is used for safely handling the change of filters capable of separating hazardous substances such as radioactive, toxic or bacterial particles and gases. A bag is arranged at an exchange opening and the filter exchange is handled inside of the bag by means of gloves being a part of the bag. There is also a compulsory demand to check that a mounted filter within the housing is leak free and conforms to the filtration class. This is done by including a probe as a part of the filter housing, and mounting the probe downstream of the filter. The probe, having an air intake and providing air samples to an analyzer, is moved in a controlled pattern as close as possible to the filter surface in order to secure a sample from a very small area of the filter at the time. It is a demand to probe a very small area if a leak should be possible to spot as an increase of concentration by the analyzer. Therefore it is desirable to have the probe mounted close to the filter surface and with an unobstructed air flow reaching the probe from the filter. This is an area of the filter housing traditionally occupied by the clamping mechanism. Mounting the clamping device on the downstream side under the filter lend itself to less complicated solutions and are widely in use, while causing air flow obstruction.
However, some efforts to move the clamping mechanism to the sides of the filter holding frame have also been made, such as in a product called BIBO filter housing of BG series, manufactured by Flanders/CSC Corporation. However, while possibly providing space for a downstream probe, the clamping mechanism has to be operated by means of a tool for turning bolt head shaped elements for loosening and tightening the clamping mechanism, which is troublesome within the bag. Furthermore, the BG series BIBO filter housing provides no clear indicator of whether the filter has been correctly positioned or not, neither before nor after clamping it.